1. Field of the Invention
This invention relates to an at least partially implantable system for rehabilitation of a hearing disorder which comprises at least one sensor (microphone) for picking up an acoustic signal and converting the acoustic signal into the corresponding electrical signals, an electronic signal processing unit for audio signal processing and amplification, an electrical power supply unit which supplies individual components of the system with current, and an output-side actoric stimulation arrangement.
2. Description of Related Art
The expression xe2x80x9chearing disorderxe2x80x9d is defined here as inner ear damage, combined inner ear and middle ear damage, and a temporary or permanent noise impression (tinnitus).
In recent years rehabilitation of sensorineural hearing disorders with partially implantable electronic systems has acquired major importance. In particular, this applies to the group of patients in which hearing has completely failed due to accident, illness or other effects or in which hearing is congenitally non-functional. If, in these cases, only the inner ear (cochlea), and not the neural auditory path which leads to the brain, is affected, the remaining auditory nerve can be stimulated with electrical stimulation signals. Thus, a hearing impression can be produced which can lead to speech comprehension. In these so-called cochlear implants (CI), an array of stimulation electrodes, which is controlled by an electronic system (electronic module) is inserted into the cochlea. This electronic module is encapsulated with a hermetical, biocompatible seal and is surgically embedded in the bony area behind the ear (mastoid). The electronic system contains essentially only decoder and driver circuits for the stimulation electrodes. Acoustic sound reception, conversion of this acoustic signal into electrical signals and their further processing, always takes place externally in a so-called speech processor which is worn outside on the body. The speech processor converts the preprocessed signals into a high frequency carrier signal which, via inductive coupling, is transmitted through the closed skin (transcutaneously) to the implant. The sound-receiving microphone is always located outside of the body and, in most applications, in a housing of a behind-the-ear hearing aid worn on the external ear. The microphone is connected to the speech processor by a cable. Such cochlear implant systems, their components, and the principles of transcutaneous signal transmission are described, by way of example, in published European Patent Application EP 0 200 321 A2 and in U.S. Pat. Nos. 5,070,535, 4,441,210, 5,626,629, 5,545,219, 5,578,084, 5,800,475, 5,957,958 and 6,038,484. Processes of speech processing and coding in cochlear implants are described for example in published European Patent Application EP 0 823 188 A1, in European Patent 0 190 836 A1 and in U.S. Pat. Nos. 5,597,380, 5,271,397, 5,095,904, 5,601,617 and 5,603,726.
In addition to rehabilitation of congenitally deaf persons and those who have lost their hearing using cochlear implants, for some time there have been approaches to offer better rehabilitation than with conventional hearing aids to patients with a sensorineural hearing disorder which cannot be surgically corrected by using partially or totally implantable hearing aids. The principle arises, in most embodiments, in stimulating an ossicle of the middle ear or, directly, the inner ear via mechanical or hydromechanical stimulation and not via the amplified acoustic signal of a conventional hearing aid in which the amplified acoustic signal is supplied to the external auditory canal. The actuator stimulus of these electromechanical systems is accomplished with different physical transducer principles such as, for example, by electromagnetic and piezoelectric systems. The advantage of these devices is seen mainly in the sound quality which is improved compared to conventional hearing aids, and, for totally implanted systems, in the fact that the hearing prosthesis is not visible.
Such partially and fully implantable electromechanical hearing aids are described, for example, by Yanigahara et al. xe2x80x9cImplantable Hearing Aidxe2x80x9d, Arch Otolaryngol Head Neck Surg-Vol 113, 1987, pp. 869-872; Suzuki et al. xe2x80x9cImplantation of Partially Implantable Middle Ear Implant and the Indicationxe2x80x9d, Advances in Audiology, Vol. 4, 160-166, Karger Basel, 1988; H. P. Zenner et al. xe2x80x9cFirst implantations of a totally implantable electronic hearing system for sensorineural hearing lossxe2x80x9d, in HNO Vol. 46, 1998, pp. 844-852; H. Leysieffer et al. xe2x80x9cA totally implantable hearing device for the treatment of sensorineural hearing loss: TICA LZ 3001xe2x80x9d, HNO Vol. 46, 1998, pp. 853-863; H. P. Zenner et al. xe2x80x9cActive electronic hearing implants for patients with conductive and sensorineural hearing lossxe2x80x94a new era of ear surgeryxe2x80x9d, HNO 45: 749-774; H. P. Zenner et al. xe2x80x9cTotally implantable hearing device for sensorineural hearing lossxe2x80x9d, The Lancet Vol. 352, No. 9142, page 1751; and are described in numerous patent documents among others in published European Patent Applications EP 0 263 254 A1, EP 0 400 630 A1, and EP 0 499 940 A1, and in U.S. Pat. Nos. 3,557,775, 3,712,962, 3,764,748, 5,411,467, 4,352,960, 4,988,333, 5,015,224, 5,015,225, 5,360,388, 5,772,575, 5,814,095, 5,951,601, 5,977,689 and 5,984,859. Here, the insertion of an electromechanical transducer through an opening in the promontory for direct fluid stimulation in the inner ear is described in U.S. Pat. Nos. 5,772,575, 5,951,601, 5,977,689 and 5,984,859.
Many patients with inner ear damage also suffer from temporary or permanent noise impressions (tinnitus) which cannot be surgically corrected and for which, to date, there are no approved drug treatments. Therefore, so-called tinnitus maskers (International Patent Application Publication WO-A 90/07251, published European Patent Application EP 0 537 385 A1, German Utility Model No. 296 16 956) are known. These devices are small, battery-driven devices which are worn like a hearing aid behind or in the ear and which, by means of artificial sounds which are emitted, for example, via a hearing aid speaker into the auditory canal, psychoacoustically mask the tinnitus and thus reduce the disturbing noise impression, if possible, to below the threshold of perception. The artificial sounds are often narrowband noise (for example, third-band noise). The spectral position and the loudness level of the noise can be adjusted via a programming device to enable adaptation to the individual tinnitus situation as optimally as possible. In addition, the so-called retraining method has been developed recently in which, by combination of a mental training program and presentation of broadband sound (noise) near the auditory threshold, the perceptibility of the tinnitus in quiet conditions is likewise supposed to be largely suppressed (H. Knoer xe2x80x9cTinnitus retraining therapy and hearing acousticsxe2x80x9d journal xe2x80x9cHoerakustikxe2x80x9d 2/97, pages 26 and 27). These devices are also called xe2x80x9cnoisersxe2x80x9d.
In the two aforementioned methods for hardware treatment of tinnitus, hearing aid-like, technical devices must be carried visibly outside on the body in the area of the ear; these devices stigmatize the wearer and, therefore, are not willingly worn.
U.S. Pat. No. 5,795,287 describes an implantable tinnitus masker with direct drive of the middle ear, for example, via an electromechanical transducer coupled to the ossicular chain. This directly coupled transducer can preferably be a so-called xe2x80x9cFloating Mass Transducerxe2x80x9d (FMT). This FMT corresponds to the transducer for implantable hearing aids which is described in U.S. Pat. No. 5,624,376.
In commonly owned co-pending U.S. patent applications Ser. Nos. 09/372,172 and 09/468,860, which are hereby incorporated by reference, implantable systems for treatment of tinnitus by masking and/or noiser functions are described, in which the signal-processing electronic path of a partially or totally implantable hearing system is supplemented by corresponding electronic modules such that the signals necessary for tinnitus masking or noiser functions can be fed into the signal processing path of the hearing aid function and the pertinent signal parameters can be individually adapted by further electronic measures to the pathological requirements. This adaptability can be accomplished by storing or programming the necessary setting data of the signal generation and feed electronics by using hardware and software in the same physical and logic data storage area of the implant system, and by controlling the feed of the masker or noiser signal into the audio path of the hearing implant via the corresponding electronic actuators.
Depending on the desired function, implantable rehabilitation devices of the aforementioned type consist of several functional units, especially: (1) a sensor (microphone) which converts the incident airborne sound into an electrical signal; (2) an electronic signal processing, amplification and implant control unit; (3) an implantable electromechanical or electroacoustic transducer which converts the amplified and preprocessed sensor signals into mechanical or acoustic vibrations and sends them via suitable coupling mechanisms to the damaged middle and/or inner ear, or, in the case of cochlear implants a cochlear stimulation electrode; and (4) an electric power supply system which supplies the aforementioned modules. Furthermore, there can be an external unit which makes available electrical recharging energy to the implant when the implant-side power supply unit contains a rechargeable (secondary) battery. Especially advantageous devices and processes for charging rechargeable implant batteries are described in commonly owned co-pending U.S. patent application Ser. No. 09/311,566 and in commonly owned U.S. Pat. No. 5,279,292, which are hereby incorporated by reference. Preferably, there can also be a telemetry unit with which patient-specific, audiological data can be wirelessly transmitted bidirectionally or programmed in the implant and thus permanently stored, as was described by Leysieffer et al. in HNO Vol. 46, 1998, pp. 853-863.
Basically, in all these at least partially implantable systems, the (audio) signal processing or signal generation and the implant control modules, such as, for example, a controlled battery recharging system or a telemetry system for bidirectional transmission of, for example, variable, patient-specific parameters are accomplished on the implant-side by permanently fixed hardware units. This also applies when digital signal processors, microcontrollers or microprocessors are used for signal processing or generation or for implant management, regardless of whether the signal processors are built as so-called xe2x80x9chardwired logicxe2x80x9d, i.e., in xe2x80x9chardwiredxe2x80x9d logic architecture, or whether their operating programs are stored in the read-only memory areas (for example, ROM) of the corresponding processors. These programs, which are provided and are necessary for basic operation of the implant and for the intended functions, are hereinafter called the operating program or the operating software. In the known implant systems, this operating software is placed in the system during production, for example, by mask programming of processor storage areas and can no longer be changed after implantation.
In contrast thereto, patient-specific data such as, for example, audiological adaptation data or variable implant system parameters (for example, a variable in one of the software programs for control of battery recharging mentioned above) are herein called operating parameters. In known totally implantable implant systems, after implantation, these operating parameters can be transmitted transcutaneously, i.e., wirelessly through the closed skin, to the implant and thus can be changed.
The above described at least partially implantable hearing systems for rehabilitation of inner ear damage which are based on an output-side electromechanical transducer, differ from conventional hearing aids essentially only in that the output-side acoustic stimulus (i.e., an amplified acoustic signal in front of the eardrum) is replaced by an amplified mechanical stimulus of the middle ear or inner ear. The acoustic stimulus of a conventional hearing aid ultimately leads to vibratory, i.e., mechanical, stimulation of the inner ear, via mechanical stimulation of the eardrum and the subsequent middle ear. The requirements for effective audio signal preprocessing are fundamentally similar or the same. Furthermore, in both embodiments on the output side a localized vibratory stimulus is ultimately routed to the damaged inner ear (for example, an amplified mechanical vibration of the stapes in the oval window of the inner ear).
Basically, in this routinely used rehabilitation of inner ear damage by active hearing systems (regardless of whether the rehabilitation is by an external acoustic stimulus or by an implanted electromechanical stimulus), at present there is a major drawback which is described below in summary for understanding of this invention: most cases of sensorineural deafness are based on more or less pronounced damage of the outer hair cells in the inner ear. These outer hair cells, which in large number are located in the organ of Corti along the basilar membrane, form part of the so-called cochlear amplifier which, depending on local excitation of the basilar membrane as a result of traveling wave formation, actively mechanically de-attenuates this local stimulation range at low levels and thus small traveling wave amplitudes, which leads to an increase in sensitivity. This active amplification is based on a very complex, efferently controlled process which is not described here. It is furthermore assumed that at very high levels of inner ear stimulation as a result of the high loudness, this effect is reversed in its action and thus locally reduces and actively attenuates the traveling wave amplitude. These nonlinear characteristics of the cochlear amplifier, which is located along the organ or Corti in several hundred functional units with locally limited action, are of decisive importance for the function of the healthy inner ear. In partial or total failure of the outer hair cells, in addition to a loss of sensitivity which leads to a rise in the hearing threshold, other disadvantages arise: the described active de-attenuation of the basilar membrane leads to high Q-factors of the envelopes of the traveling waves (tuning curves) which are essentially responsible for the frequency differentiation capacity (tone pitch differences). If this high quality is lacking due to failure or partial damage of the outer hair cells, the affected individual can perceive tone pitch differences much more poorly. The rise of the hearing threshold leads, moreover, to a reduction of the dynamic range since the upper sensory boundary (discomfort threshold) in labyrinthine deafness does not rise at the same time. This reduction of dynamics results in an increased perception of loudness which is called positive recruitment. The described effects, which arc caused by damage or failure of the outer hair cells, lead, in the overall effect for the affected individual, to a reduction in speech comprehension, especially in a noisy environment (summary description in Zenner, H. P.: Hearing, Georg Thieme Verlag Stuttgart, New York, 1994, pages 20-23, 107 and 108, and LePage, E. W., Johnstone, M. B.: xe2x80x9cNon-linear mechanical behavior of the basilar membrane in the basal turn of the guinea pig cochlea.xe2x80x9d Hearing Research 2 (1980), pp. 183-189).
An important consequence of this described mechanism is that, as indicated above, both in conventional acoustic hearing aids and also in partially or fully implantable hearing systems, the important functions of the damaged outer hair cells and thus of the cochlear amplifier cannot be replaced or at least partially restored. U.S. Pat. No. 6,123,660 discloses a converter arrangement for partially or fully implantable hearing aids for direct mechanical excitation of the middle ear or inner ear, which is provided with a piezoelectric converter element and also with an electromagnetic converter which are accommodated in a common housing and the two can be coupled via the same coupling element to the middle ear ossicle or directly to the inner ear. Furthermore, implantable hearing systems are known (U.S. Pat. No. 5,997,466, 6,005,955) which work with two or more output-side electromechanical converters in one or locally separate arrangements. These embodiments are, however, uniquely described in that a system design with more than one converter enables a linear superposition of the deflection frequency responses of the individual converters which, as a result, allows an output-side excitation form of the cochlea which is adjustable or programmable depending specifically on frequency or spectrally optimized as much as possible and thus will lead to a spectrally balanced and sufficient loudness impression of the implant system. Rehabilitation of the cochlear amplifier with the aforementioned features is, however, not possible by these embodiments or described signal preprocessing methods.
In cochlear implants (CI), solely electrical stimulation signals are now used as the actuator stimuli. After implantation of a CI in completely deaf patients, training is generally necessary for rehabilitation of hearing, since the artificial stimuli must be learned, because the artificial stimuli do not fundamentally correspond to the biologically proper form of stimulation of the inner ear. Conversely, this rehabilitation phase is omitted after implantation of an electromechanical hearing system in those with hearing difficulties since the mechanical form of stimulation is biologically suitable, as described above, and since the mechanical form of stimulation ultimately largely corresponds with a hearing aid at least with respect to the basic function, i.e., the stimulation at the input of the inner ear is of a vibratory nature.
For the aforementioned reasons, implantable electromechanical systems cannot be employed for hearing disorders which approach deafness. Here, cochlear implants with purely electrical stimulation of the inner ear may be considered which of course do not promise sound quality which for example would enable acceptable music transmission, but which rather are primarily designed for acquiring or restoring sufficient speech comprehension, as much as possible without lip reading. As a result of the electrical stimulation, as described, hearing losses which extend to complete deafness are possible in a spectrally wide audiological range.
Recently it has become scientifically known from CI implantations that even for incomplete deafness cochlear implants (CIs) can be successfully used when sufficient speech discrimination can no longer be achieved with a conventional hearing aid. Interestingly it was demonstrated that the important inner ear structures which enable residual acoustic hearing capacity can be maintained in part or largely stably over time when a CI electrode is inserted into the cochlea (S. Ruh et al.: xe2x80x9cCochlear implant for patients with residual hearingxe2x80x9d, Laryngo-Rhino-Otol. 76 (1997) pp. 347-350; J. Mueller-Deile et al.: xe2x80x9cCochlear implant supply for non-deaf patients?xe2x80x9d Laryngo-Rhino-Otol. 77 (1998) pp. 136-143; E. Lehnhardt: xe2x80x9cIntracochlear placement of cochlear implant electrodes in soft surgery techniquexe2x80x9d, HNO 41 (1993), pp. 356-359). In the foreseeable future it certainly will be possible, in case of residual hearing capacity, to clinically place CI electrodes intracochlearly in a manner such that the remaining inner ear structures can be preserved over the long term and thus can continue to be stimulated in a biologically proper manner, i.e., vibrationally, and lead to a usable hearing impression.
The object of the invention is to devise an at least partially implantable system for rehabilitation of a hearing disorder which can be matched especially effectively and flexibly to the individual pathological and audiological situation of the respective patient.
This object is achieved in that, in an at least partially implantable system for rehabilitation of a hearing disorder which comprises at least one sensor (microphone) for picking up an acoustic signal and converting the acoustic signal into corresponding electrical signals, an electronic signal processing unit for audio signal processing and amplification, an electrical power supply unit which supplies individual components of the system with current, and an output-side actuator stimulation arrangement, as the actuator stimulation arrangement there is a dual intracochlear arrangement which in combination has a stimulator arrangement with at least one stimulator element for at least indirect mechanical stimulation of the inner ear and an electrically acting stimulation electrode arrangement with at least one cochlear implant electrode for electrical stimulation of the inner ear.
With the system both stimulation methods, i.e., the use of mechanical and electrical stimulation, can be used in a single implant system and can be applied patient-specifically depending on the individual audiological situation (xe2x80x9cdualxe2x80x9d hearing implant). Direct stimulation of the cochlea prevents or largely reduces the occurrence of feedback, i.e., coupling of the output signal into the sensor (microphone) because the ossicle chain and thus the eardrum are not excited to vibrations or at least are to a reduced degree. This is especially advantageous when an acoustic sensor (microphone function) is applied in the immediate vicinity of the eardrum, as is known from U.S. Pat. Nos. 5,814,095 and 5,999,632. Therefore, overall with this implant system the use of a combined xe2x80x9cdualxe2x80x9d output-side converter array circumvents or at least reduces the indicated drawbacks of a purely electromechanically acting hearing system and of a purely electrically acting implantable CI such that by the combined action of the two forms of stimulation and individually maximized parameter adjustment of the controlling electronic preprocessing system on the one hand an indication position as audiologically wide as possible and on the other hand in individual patients a result as optimum as possible with respect to speech discrimination, sufficient loudness in all relevant spectral ranges and high sound quality are achieved.
The stimulator arrangement can advantageously have at least one intracochlear electromechanical converter for direct mechanical stimulation of the inner ear and/or at least one intracochlear hair cell stimulating electrode for indirect mechanical stimulation of the inner ear by electrical stimulation of the outer hair cells. Preferably there is an intracochlear array with several stimulator elements for direct and/or indirect mechanical stimulation of the inner ear which can be implanted directly into the fluid-filled space of the inner ear (scala tympani or scala vestibuli) just like a cochlear implant electrode array which is provided preferably with a plurality of cochlear implant electrodes.
The hair cell stimulation electrodes intended for indirect mechanical stimulation of the inner ear are preferably made such that in the implanted state the hair cell stimulation electrodes come to rest in the immediate vicinity of the outer hair cells. Here the circumstance is used that the outer hair cells react mechanically with changes in length when the outer hair cells are artificially stimulated by electricity. These dynamic elongations are synchronous with the electrical stimulation signal up to very high frequencies which can extend to above the audiological range to be supplied. In this way, similarly to when using intracochlear electromechanical converters, electrical stimulation forms achieved on the output side for example by means of cochlear implant electrodes can be combined with mechanical cochlear stimulations because the outer hair cells are directly operated as xe2x80x9celectromechanical convertersxe2x80x9d as takes place in a healthy, undamaged inner ear biologically by neural efferent triggering. This application is especially suitable for pathological cases in which only the outer hair cells are damaged for example by ototoxic medications, i.e., the outer hair cells can no longer perform their neural transmitter function or can only do so to a limited degree, the stereocilia which xe2x80x9cmechanicallyxe2x80x9d join the hair cells to the tectorial membrane are however undamaged or intact to such an extent that there is reliable mechanical coupling to the tectorial membrane stable over the long term.
The cochlear implant electrode(s) intended for direct electrical stimulation of the inner ear is (are), as is known in the prior art for cochlear implants, feasibly embedded in the carrier or fixed or on the carrier such that in the implanted state a portion of the surface of each stimulation electrode is in direct galvanic contact with the lymphatic fluid of the inner ear or directly with one of the neural structures to be stimulated.
There can be a common carrier for the cochlear implant electrode(s) and the electromechanical converter(s), the electromechanical converter(s) and the cochlear implant electrode(s) being arranged advantageously along the carrier alternating in one another. In this way mechanical wave propagation within the carrier between adjacent electromechanical converter elements can be damped and locally concentrated mechanical stimulation per converter can be achieved.
However, there can also be separate carriers for the cochlear implant electrode(s) and the electromechanical converter(s). In this case, the carrier for the cochlear implant electrode(s) is arranged such that in the implanted state the carrier is oriented to the inside with reference to the cochlea, in order to lie as near as possible to the neural structure (modiolus) to be stimulated.
The dual intracochlear arrangement preferably has a total diameter in the range of 0.4 mm (apical area) to 2.0 mm (basal area) and a total length between 5 mm and 50 mm. The carrier or carriers advantageously comprise a biocompatible material which is biostable in the inner ear, preferably a polymer, especially a silicone. The individual electromechanical converters can be embedded in the carrier for reasons of biocompatibility such that the individual electromechanical converters are completely surrounded by a thin layer of the carrier material.
In order to minimize mechanical wave propagation from a converter within the carrier to adjacent converters, in another embodiment of the invention between the individual output-side electromechanical converters mechanical attenuation elements are embedded in the carrier, the material of the attenuation elements for a similar cross sectional geometry to that of the carrier being preferably chosen such that to achieve high attenuation values there is a high mechanical impedance difference compared to the carrier material. As already mentioned, optionally the cochlear implant electrodes can moreover be used as attenuation elements.
The electromechanical converter(s) is (are) preferably made hermetically sealed and the electromechanical converter(s) can work fundamentally according to any known electromechanical converter principle, and can be made especially as electromagnetic, electrodynamic, piezoelectric, magnetostrictive or dielectric (capacitive) converters. When using the piezoelectric converter principle the electromechanical converter(s) is (are) advantageously made using PZT ceramic (lead zirconate titanate) or PVDF (polyvinylidene fluoride), preferably using geometrical shape transformations, especially the bimorph principle, the unimorph principle or the heteromorph principle with passive material partners such that at a given converter voltage the electromechanical converter(s) produce maximum deflection with minimum electric power consumption.
In another embodiment of the invention, several stimulator elements for at least indirect mechanical stimulation of the inner ear are arranged distributed equidistantly or at logarithmic distances according to the tonotopic frequency-location assignment along the basilar membrane of the inner ear, and in the case of a tonotopic arrangement of stimulator elements for mechanical stimulation of the inner ear 20 to 24 stimulator elements or groups of stimulator elements can lead to especially favorable results according to psychoacoustic critical bands.
The electromechanical converter(s) feasibly has (have) a transmission range from roughly 100 Hz to roughly 10 kHz and electromechanical converter(s) is (are) preferably highly tuned, i.e., the first mechanical resonant frequency is at the upper end of the desired transmission frequency range, especially at roughly 8 kHz to roughly 10 kHz. This results in that the deflection frequency response of the converters in the transmission range is largely free of resonances and for voltage impression and the use of piezoelectric converters is flat regardless of frequency. Thus there is no ripple in the transmission range.
The cochlear implant electrode(s) and/or the hair cell stimulation electrode(s) can comprise all known biocompatible metals, especially pure platinum, preferably platinum-iridium alloys (preferably 90% Pt, 10% Ir), pure gold, gold alloys, tantalum, tantalum alloys, niobium, niobium alloys and high quality steels.
The signal processing unit feasibly has a preprocessing arrangement for pre-amplification and/or filtering and for analog-digital (A/D) conversion of the acoustic sensor signals. The signal processing unit can in particular comprise anti-aliasing filters. In the presence of several acoustic sensors preferably each of the acoustic sensors is upstream of its own analog-digital converter.
In another embodiment of the invention, the signal processing unit can contain software modules which parallel to operation of the hearing aid enables masking of tinnitus. With this multichannel hearing implant system, tinnitus which can be at least peripherally localized can be masked more effectively than with known conventional tinnitus maskers.
The signal processing unit advantageously has a digital signal processor for processing the A/D-converted acoustic sensor signals which have been optionally preprocessed by means of the preprocessing arrangement and/or for generation of digital signals for tinnitus masking, at least one analog-digital converter being assigned to the actuator stimulation arrangement and preferably upstream of the stimulator element(s) for at least indirect mechanical stimulation of the inner ear and the cochlear implant electrode(s) for electrical stimulation of the inner ear its own digital-analog converter being located.
In another embodiment of the invention, the signal processing electronics contains software modules which trigger the stimulator element(s) for at least indirect mechanical stimulation of the inner ear, therefore especially the intracochlear electromechanical converters which directly mechanically excite the inner ear and/or the hair cell stimulation electrodes which mechanically excite the inner ear in interaction with the outer hair cells, such that the spectral, time, amplitude- and phase-referenced properties of the signals which trigger the stimulator elements are dimensioned such that a traveling wave is produced on the basilar membrane of the damaged inner ear which is as near as possible to that of healthy hearing.
The software modules can be designed to be static such that as a result of scientific findings the software modules are filed once in the program storage of the digital signal processor and remain unchanged. But then if later for example due to more recent scientific findings improved algorithms for speech signal processing are available and these improved algorithms are to be used, the entire implant or implant module which contains the corresponding signal processing unit must be replaced by a new unit with the altered operating software by invasive surgery on the patient. This surgery entails renewed medical risks for the patient and is very complex.
This problem can be solved in that, in another embodiment of the invention, a wireless, preferably PC-based telemetry means is provided for transmission of data between the implanted part of the system and an external unit, especially an external programming system, a rewritable implantable storage arrangement is assigned to the signal processor for accommodating and reproducing the operating program and at least parts of the operating program can be replaced or changed by data transmitted from the external unit via the telemetry means. In this way, after implantation of the implantable system the operating software as such can be changed or completely replaced, as is explained for otherwise known systems for rehabilitation of hearing disorders in U.S. Pat. No. 6,198,971.
In addition, the design of totally implantable systems preferably is such that, in a manner known per se, after implantation also operating parameters, i.e., patient-specific data, for example audiological adaptation data, or variable implant system parameters (for example, a variable in a software program for control of battery recharging), can be transmitted transcutaneously, i.e., wirelessly through the closed skin, to the implant and can thus be changed. In such a case the software modules are designed to be preferably dynamic, or in other words, adaptive, in order to rehabilitate the hearing disorder as optimally as possible. In particular the software modules can be designed to be adaptive, and parameter matching can be accomplished by training by the implant wearer and using other aids.
Furthermore, the signal processing electronics can contain a software module which achieves simulation of a xe2x80x9chealthyxe2x80x9d cochlear amplifier as optimum as possible based on an adaptive neural network. Training of this neural network can take place again by the implant wearer and/or using other external aids. Especially in the neural network for simulation of a xe2x80x9chealthyxe2x80x9d cochlear amplifier the principle of time-reversed acoustics (TRA) can be implemented, and triggering of the output-side electromechanical converters can take place by TRA such that locally limited areas of the cochlea are mechanically stimulated.
The storage arrangement for storage of operating parameters and the storage arrangement for holding and reproducing the operating program can be implemented as storages independent of one another; however there can also be a single storage in which both the operating parameters and also operating programs can be filed.
The storage arrangement for storage of operating parameters and the storage arrangement for storage and retrieval of the operating program can be implemented as storages independent of one another; however there can also be a single storage in which both the operating parameters and also operating programs can be filed.
This approach allows matching of the system to circumstances which can be detected only after implantation of the implantable system. Thus, for example, in an at least partially implantable hearing system for rehabilitation of a monaural or binaural inner ear disorder and of a tinnitus by mechanical stimulation of the inner ear, the sensoric (acoustic sensor or microphone) and actoric (output stimulator) biological interfaces are always dependent on anatomic, biological and neurophysiological circumstances, for example on the interindividual healing process. These interface parameters can also be individual, also especially time-variant. Thus, for example the transmission behavior of an implanted microphone can vary interindividually and individually as a result of being covered by tissue, and the transmission behavior of an electromechanical transducer which is coupled to the inner ear can vary in view of on different coupling qualities. These differences of interface parameters which cannot be eliminated or reduced in the devices known from the prior art even by replacing the implant can now be optimized by changing or improving the signal processing of the implant.
In an at least partially implantable hearing system, it can be advisable or become necessary to implement signal processing algorithms which have been improved after implantation. Especially the following should be mentioned here:
speech analysis processes (for example, optimization of a fast Fourier transform (FFT))
static or adaptive noise detection processes
static or adaptive noise suppression processes
processes for optimization of the signal to noise ratio within the system
optimized signal processing strategies in progressive hearing disorder
output level-limiting processes for protection of the patient in case of implant malfunctions or external faulty programming
processes of preprocessing of several sensor (microphone) signals, especially for binaural positioning of the sensors
processes for binaural processing of two or more sensor signals in binaural sensor positioning, for example optimization of spacial hearing or spacial orientation
phase or group delay time optimization in binaural signal processing
processes for optimized driving of the output stimulators, especially for binaural positioning of the stimulators.
Among others, the following signal processing algorithms can be implemented with this system even after implantation:
processes for feedback suppression or reduction
processes for optimization of the operating behavior of the output transducer(s) (for example, optimization of the frequency response and phase response, improvement of the impulse response)
speech signal compression processes for sensorineural hearing loss
signal processing methods for recruitment compensation in sensorineural hearing loss.
Furthermore, in implant systems with a secondary power supply unit, i.e., a rechargeable battery system, but also in systems with primary battery supply it can be assumed that these electrical power storages will enable longer and longer service lives and thus increasing residence times in the patients as technology advances. It can be assumed that fundamental and applied research for signal processing algorithms will make rapid progress. The necessity or the patent desire for operating software adaptation and modification will therefore presumably take place before the service life of the implanted power source expires. The system described here allows this adaptation of the operating programs of the implant even when the implant has already been implanted.
Preferably, there can furthermore be provided a buffer storage arrangement in which data transmitted from the external unit via the telemetry means can be buffered before being relayed to the signal processor. In this way the transmission process from the external unit to the implanted system can be terminated before the data transmitted via the telemetry means are relayed to the signal processor.
Furthermore, there can be provided checking logic which checks the data stored in the buffer storage arrangement before relaying the data to the signal processor. There can be provided a microprocessor module, especially a microcontroller, for control of the A/D-converters and/or the D/A converters and/or the signal processor within the implant via a data bus, preferably the checking logic and the buffer storage arrangement being implemented in the microprocessor module, and wherein also program parts or entire software modules can be transferred via the data bus and the telemetry means between the outside world, the microprocessor module and the signal processor.
An implantable storage arrangement for storing the working program for the microprocessor module is preferably assigned to the microprocessor module, and at least parts of the working program for the microprocessor module can be changed or replaced by data transmitted from the external unit via the telemetry means.
In another embodiment of the invention, at least two storage areas for storage and retrieval of at least the operating program of the signal processor may be provided. This contributes to the reliability of the system, in that due to the multiple presence of a storage area which contains the operating program(s), for example, after transmission from the exterior or when the implant is turned on, checking for the absence of faults in the software can be done.
Analogously to the above, the buffer storage arrangement can also comprise at least two storage areas for storage and retrieval of data transferred from the external unit via the telemetry means, so that after data transmission from the external unit still in the area of the buffer storage the absence of errors in the transferred data can be checked. The storage areas can be designed for example for complementary filing of the data transferred from the external unit. At least one of the storage areas of the buffer storage arrangement however can also be designed to store only part of the data transferred from the external unit, wherein in this case the absence of errors in the transferred data is checked in sections.
Furthermore, to ensure that in case of transmission errors, a new transmission process can be started, a preprogrammed read-only memory area which cannot be overwritten can be assigned to the signal processor, in which ROM area the instructions and parameters necessary for xe2x80x9cminimum operationxe2x80x9d of the system are stored, for example, instructions which after a xe2x80x9csystem crashxe2x80x9d ensure at least error-free operation of the telemetry means for receiving an operating program and instructions for its storage in the control logic.
As already mentioned, the telemetry means is advantageously designed not only for reception of operating programs from the external unit but also for transfer of operating parameters between the implantable part of the system and the external unit such that on the one hand such parameters (for example the volume) can be adjusted by a physician, a hearing aid acoustics specialist or the wearer of the system himself, and on the other hand the system can also transfer the parameters to the external unit, for example to check the status of the system.
A totally implantable hearing system of the aforementioned type can have on the implant side in addition to the actoric stimulation arrangement and the signal processing unit at least one implantable acoustic sensor and a rechargeable electrical storage element, and in this case a wireless transcutaneous charging device can be provided for charging of the storage element. For a power supply there can also be provided a primary cell or another power supply unit which does not require transcutaneous recharging. This applies especially when it is considered that in the near future mainly by continuing development of processor technology a major reduction in power consumption for electronic signal processing can be expected so that for implantable hearing systems new forms of power supply will become usable in practice, for example power supply which uses the Seebeck effect, as is described in U.S. Pat. No. 6,131,581. Preferably, there is also provided a wireless remote control for control of the implant functions by the implant wearer.
In case of a partially implantable hearing system, at least one acoustic sensor, an electronic signal processing arrangement, a power supply unit and a modulator/transmitter unit are contained in an external module which can be worn outside on the body, especially on the head over the implant. The implant comprises the output-side electromechanical transducer and the intracochlear stimulation electrode array, but is passive in terms of energy and receives its operating energy and transducer control data via the modulator/transmitter unit in the external module.
The described system can be designed to be monaural or binaural for the fully implantable design as well as for the partially implantable design. A binaural system for rehabilitation of a hearing disorder of both ears has two system units which each are assigned to one of the two ears. In doing so the two system units can be essentially identical to one another. However, one of the system units can also be designed as a master unit and the other system unit as a slave unit which is controlled by the master unit. The signal processing modules of the two system units can communicate with one another in any way, especially via a wired implantable line connection or via a wireless connection, preferably a bidirectional high frequency path, a ultrasonic path coupled by bone conduction, or a data transmission path which uses the electrical conductivity of the tissue of the implant wearer such that in both system units optimized binaural signal processing and transducer array control are achieved.
These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, shows several embodiments in accordance with the present invention.